How Parsers Handle Namespaces

Namespaces were added to XML 1.0 after the fact, but care was taken to
ensure backwards compatibility.

An XML 1.0 parser that does not know about namespaces will most likely
not have any troubles reading a document that uses namespaces.

A namespace aware parser also checks to see that all prefixes are
mapped to URIs. Otherwise it behaves almost exactly like a non-namespace
aware parser.

Other software that sits on top of the raw XML parser, an XSLT engine
for example, may treat elements differently depending on what namespace
they belong to. However, the XML parser itself mostly doesn't care as long
as all well-formedness and namespace constraints are met.

A possible exception occurs in the unlikely event that elements with
different prefixes belong to the same namespace or elements with the same
prefix belong to different namespaces

Many parsers have the option of whether to report namespace violations so
that you can turn namespace processing on or off as you see fit.